Let's talk metal fatigue with solid mounts

[MikeE36]

Hey guys, another noob question here.. I have never built a race car, or a dedicated track car for that matter. I currently run all powerflex bushings in my turbo M3 that recently was wrecked into by a drunk driver. I am doing a full drivetrain swap into Collin's caged E36 shell (M3_Muscle). This will be a dedicated track car and will not see street use to speak of. The subframe pickup points front and rear have been reinforced, but I am wondering about fatiguing the unibody over time with solid subframe, trans, and engine mounts.

I had Vorshlag nylon engine mounts in my car for a short period of time and felt the vibration was so significant that I felt I would rattle something loose and cause a problem, so I switched back to stock. Now that I am building a 100% track car, I am not as worried, but still have concerns.

How many of you have track cars or race cars with all solid mounts? Have you had metal fatigue issues / failures over the years of track / race abuse? I do not want to put all aluminum bushings and spherical bearings everywhere, only to have unibody cracks and a ton of other issues with 2-3 years of use. I may be worrying about nothing, but with 900 lb springs in the rear, my car already feels fairly stiff. I can imagine it is going to feel much more direct with all the seam welding and the extensive cage collin has fabricated, along with all solid mounts. Are solid mounts pretty much a "go-to" or "obvious" part for a race car, or do some of you guys run poly still? Advice on subframe / rtab / engine / trans mounts would be great for a track-only car, that sees lots of use on bumpy Texas tracks.

-Mike

[SG_M3]

Reinforce the mounts, run solid where you can. Bearing rtabs are awesome, and I'd have no second thoughts about solid aluminum motor, trans, and diff mounts.

[jmitro]

agreed.
if the pickup points are reinforced and tied into the cage (which they are for Collin's car) then the loads are transmitted to the cage rather than unibody, so fatigue should be kept to a minimum (disclaimer....I'm no engineer )

I used to have full rear coilovers on my E36 so all the weight was transmitted directly to the upper shock mounts which were heavily reinforced and tied into the cage. I had no concerns over upper mount failure. Only reason I went back to stock location rear springs was concern over the lower shock bolt failing.